How to re-use encrypted volume

[Josef Wolf]

Hello,

With ubuntu-8.10, I had created an encrypted data partition on my laptop
to protect privacy in case it would be stolen (or lost, or whatever).

Now, I'd like to install 9.10 (I use the alternate CD for installation),
but re-use that data partition. When I enter the "configure crypted volumes"
menu, I select the partition, then I enter the passphrase, and then I get
an error message saying that configuration failed.

So how am I supposed to re-use an existing encrypted volume?

Any hints?